1. Field of the Invention
The invention relates to a method and apparatus for digital video processing, more particularly to a method and apparatus for displaying resized pictures on an interlaced target display system.
2. Description of the Related Art
Presently, pictures in a video compact disc (VCD) title are generally encoded in one of the following three source-input formats (SIF) 352xc3x97240 at 29.97 Hz; 352xc3x97240 at 23.976 Hz; and 352xc3x97288 at 25 Hz. Different formats are used in different source materials that were published in different areas of the globe to match the television system adopted by the particular area. For example, the 352xc3x97240 at 29.97 Hz scan format is adopted by programs suitable for the NTSC system, which is widely used in North America and Japan. The 352xc3x97240 at 23.976 Hz scan format is adopted for motion picture films. The 352xc3x97288 at 25 Hz scan format, which offers a higher picture height, is adopted by programs suitable for the PAL system that is popular in both Europe and China. Since it is desirable for the published video CD to be exchangeable worldwide, the video CD player must be made to allow the display of the aforementioned video formats on different television system specifications.
The two most popular commercial television system specifications in the world are the NTSC and PAL scan formats. The NTSC scan format has a vertical refresh rate of 59.94 Hz, whereas the PAL scan format has a vertical refresh rate of 50 Hz. Both scan formats use interlaced scanning to reduce flicker. In order to target a video CD title for display on these two television systems, it is inevitable to enhance the picture elements to reach the scan resolution required by the two systems. For example, the SIF picture resolution is at least required to be increased to two times in both vertical and horizontal directions. Thus, in a typical NTSC television system, the usual frame resolution is 704xc3x97480 at 29.97 Hz, and this frame is split into odd and even fields, each for scanning within a field rate of 1/59.94 Hz.
In addition to the spatial resolution enhancement, there is also a need to adapt the temporal resolution to another format so as to avoid jittering due to differences in the frame rate and scan rate between the encoded video CD title and the target display system. This action is called frame rate conversion and makes it possible to display NTSC-encoded frames on a PAL television system, and vice versa. In general, frame rate conversion is needed for video CD titles involving the aforementioned three kinds of SIF scan formats to permit display on both NTSC and PAL television monitors.
A well-known 3:2 pull-down technique is used as a conversion for targeting motion picture film titles on an NTSC display since a 5-field time period of the NTSC display is equal to the time period of two motion picture film frames. As such, one motion picture film frame is displayed over two consecutive fields, followed by the display of the other motion picture film frame over three consecutive fields, so that motion picture film frames can be played back smoothly on the NTSC display. However, the 3:2pull-down technique uses identical picture contents to be repeated for the corresponding two fields and three fields for two consecutive motion picture film frames. This will result in a picture-shaking phenomenon when the frames are applied to an interlaced display device.
Therefore, to display SIF-formatted video CD frames on a target television system of 625-lines/50 HZ (PAL) or 525-lines/59.94 Hz (NTSC) that have 576 and 480 active lines respectively in a frame time, there is a need to modify the picture size as well as the frame rate for various formatted titles to suit the interlaced display device and to provide enough resolution from a spatial point of view and maintain continuity of motion from a temporal point of view.
The object of the present invention is to provide a method and apparatus for displaying SIF-encoded source pictures on an interlaced television system for enriching the resolution, reducing line flicker, preserving picture aspect ratio, and maintaining good continuity of motion.
According to one aspect of the invention, a method for displaying resized pictures on an interlaced target display system comprises: reading contents of an input video source; decoding the contents of the input video source to obtain original input picture data and title format information that indicates scan format of the original input picture data; identifying television system specification of the interlaced target display system; according to the scan format of the original input picture data and the television system specification of the interlaced target display system, performing a resizing operation to resize the original input picture data and obtain resized frames having a frame size sufficient for division into even and odd fields with field size characteristics that comply with the television system specification of the interlaced target display system; storing the resized frames in a resize memory; and according to the scan format of the original input picture data and the television system specification of the interlaced target display system, controlling the resize memory to output the resized frames in the form of the even and odd fields with a timing sequence that complies with field scanning characteristics of the television system specification of the interlaced target display system.
According to another aspect of the invention, an apparatus for displaying resized pictures on an interlaced target display system comprises a video input unit, a video decoder unit, a target system selector, a resize filter, a resize memory and a display controller. The video input unit is adapted to read contents of an input video source. The video decoder unit is connected to the video input unit, and is adapted to decode the contents of the input video source from the video input unit to obtain original input picture data and title format information that indicates scan format of the original input picture data. The target system selector is operable so as to generate a select signal to identify television system specification of the interlaced target display system. The resize filter is connected to the video decoder unit and the target system selector, and receives the title format information and the select signal therefrom. The resize filter performs a resizing operation to resize the original input picture data from the video decoder unit and obtain resized frames having a frame size sufficient for division into even and odd fields with field size characteristics that comply with the television system specification of the interlaced target display system. The resize memory is connected to the resize filter for storing the resized frames therein. The display controller is connected to the video decoder unit and the target system selector, and receives the title format information and the select signal therefrom. The display controller is further connected to and controls the resize memory to output the resized frames in the form of the even and odd fields with a timing sequence that complies with field scanning characteristics of the television system specification of the interlaced target display system.